Nowadays, human hair is treated with hair care cosmetic preparations in various ways. Including, for example, cleansing the hair with shampoos, nourishing and regenerating with conditioners and masks, as well as bleaching, dyeing and changing the shape of hair with dyes, toning agents, perming agents and styling preparations. Agents for changing or tinting the color of the hair plays a role in such methods. Apart from blonding agents, which decompose natural hair dyes to achieve an oxidative lightening, oxidative hair dyeing is useful to changing the color of hair.
To achieve permanent, intense colors with corresponding fastness properties, so-called oxidative dyes are used. Said dyes may contain oxidative dye precursors, also referred to as developer components and coupler components. The developer components join together or couple with one or more coupler components to form, under the influence of oxidants or atmospheric oxygen, the actual colorants per se. To achieve natural-looking colors, a mix from a large number of oxidative dye precursors (referred to below as OFV) may be used; in many cases, substantive dyes (referred to below as DZ) are still used for tinting.
Oxidative dyes for stabilization of dye precursors during storage and to accelerate reaction during the oxidative use may have an alkaline pH value that is adjusted with alkalizing agents, such as alkanolamines, ammonia or inorganic bases.
The aforementioned oxidation dye precursors (OFV) and alkalizing agents are often incorporated into a cosmetically suitable carrier, such as a cream or a gel. The carrier aides homogeneous distribution and an adequate dwell time of the oxidative dye on the hair.
Commercial oxidative dyes are often formulated in product series including a standardized carrier, which can be combined with the tint-specific OFV combination and alkalizing agents largely without limitation.
Consumers can refer to the hair coloration achievable by employing a hair dye from information on the hair dye packaging and/or from a color chart enclosed with the packaging. For the consumer, it is desirable that the result of the coloration is as close as possible to the color indicated by the manufacturer.
Therefore, hair dyes are tested for the achievable color and also for a multiplicity of application properties ahead of the market launch. However, such tests consider the interactions between OFV and also, where applicable, between DZ and the standardized carrier only for a specific, standardized carrier. The manufacturers regularly require that a hair dye series is matched specifically to the particular needs of certain user groups. This is achieved by adding the corresponding active ingredients or nourishing agents to the standardized carrier. For consumers with severely damaged hair, the addition of one or several nourishing agent(s) with a repairing effect, for example, is recommended; for consumers with fine hair, the addition or one or several active ingredient(s) that strengthen the hair structure is recommended.
However, the result of the dyeing process depends not solely on the combination of OFV and, where applicable DZ, used. It is also influenced by the constituents of the carrier. For example, the addition of nourishing agents and active ingredients to the standardized carriers can lead to a change in the capacity of the dye formed under the influence of the oxidant and/or the partially-oxidizing dye to coat the keratinous fibers and hence to a stronger color change result than that achieved by the standardized carrier.
Such color differences and/or changed color results are described by the present application as “color shift”. This color shift, also referred to as dE or ΔE, can be determined by colorimetry by employing a colorimeter, which measures the colors in the L*,a*,b* color space by employing a colorimeter from Datacolor, Type Spectraflash 450, for example.
The L*,a*,b* color space means the CIELAB color space. The L-value denotes the lightness of the color (black-white axis); the higher the value for L, the lighter the color. The a-value denotes the red-green axis of the system; the higher this value, the more the color is shifted into the red. The b-value denotes the yellow-blue axis of the system; the higher this value, the more the color is shifted into the yellow.
The color shift ΔE, i.e. the color difference between two (hair) colors, for which a L*,a*,b* value combination was determined in each case, is calculated according to the following formula:ΔE=((Li−L0)2+(ai−a0)2+(bi−b0)2)1/2 a0, b0 and L0 are the L*, a* and b* values of the hair strands colored using the standardized carrier, whereas ai, bi and Li are the L*, a* and b* values, which are obtained for coloration using nourishing agents and/or active ingredients in the standardized carrier. The greater the value for ΔE, the more pronounced the color difference or “color shift”. Color differences with an ΔE< about 1 are not perceptible to the human eye. Color differences with an ΔE< about 2 are visible only to the trained eye. Color differences with an ΔE> about 2 are visible even to the untrained eye.
In the worst case, the addition of an additive to a standardized carrier causes a color shift, compared to the standard carrier without additives, of ΔE> about 2, which is visible to even the consumer's untrained eye. To avoid extensive tests with respect to the achievable hair coloration and, where applicable, the fastness properties having to be carried out every time additives are added to standard carriers, it is therefore desirable to identify active ingredients and nourishing agents for the hair, the addition of which causes no or at least only a minimal color shift.
The present disclosure therefore addressed the problem of providing cosmetic agents for changing the color of keratinous fibers, said agents containing one or more selected nourishing agents and active ingredients, which cause no or only a minimal color shift.